Pakistani President Asif Ali Zardari prevailed upon the U.N. Tuesday to delay the release for two weeks of a fact-finding report that is expected to criticize Pakistan's security establishment for its handling of the December 2007 assassination of his wife, former Prime Minister Benazir Bhutto.

The move represents a political retreat by the Pakistani leader, who requested the U.N. probe during his first weeks in office, but is now facing challenges to his authority on several fronts. The Pakistani parliament is moving to strip him of powers he inherited from Pakistan's military government, and Pakistan's Supreme Court is set to reopen a pair of corruption cases against him.

The United Nations announced the delay just about two hours before a three-member U.N. fact-finding commission was scheduled to release a report on Bhutto's assassination in a press conference at U.N. headquarters.

But U.N. Secretary-General Ban Ki-moon "accepted an urgent request by the president of Pakistan" to put off the release until April 15, according to Martin Nesirky, Ban's chief spokesman. Nesirky provided no explanation as to why Zardari asked to put off the release of the report, which has not been presented to Ban or the Pakistani government. He said the U.N. commission had informed Ban that its report is "complete and ready to be delivered."

Pakistan sought to use the delay to get the U.N. to reopen the investigation to consider new evidence. Pakistan's presidential spokesman, Farhatullah Babar, told the Associated Press that the U.N. commission should question two unidentified heads of state he claimed had called Bhutto before her death to warn of "serious threats to her life." But the U.N. insisted that the investigation was complete and there was no need to pursue new leads.

The U.N. commission, headed by Chile's U.N. ambassador, Heraldo Muñoz, has conducted a nine-month long inquiry into the circumstances surrounding the Dec. 27, 2007, attack that killed Bhutto after an election campaign rally in Rawalpindi. Bhutto's murder, just 10 weeks after her return from exile, sparked riots throughout Pakistan.

The report does not place blame on individuals for ordering Bhutto's killing, according to U.N. officials. But it sharply criticizes the Pakistan military for furnishing Bhutto with inadequate security on the day of her murder. It also faults Pakistan's former military government for allowing the crime scene and Bhutto's vehicle to be washed shortly after the killing.

A senior U.N.-based diplomat, who has met with members of the commission, said the report was also consistent with the findings of a Scotland Yard team that concluded Bhutto was killed by a single suicide bomber who blew up her vehicle. The team did not determine whether someone had ordered the killing.

The abrupt, last-minute appeal for a delay by Zardari comes about 18 months after the Pakistani leader made a personal appeal to Ban to conduct a wide-ranging probe into his late wife's murder. At the time, Zardari said he was less interested in holding the killers accountable than in having the United Nations produce an exhaustive document that honors his wife's democratic crusade in the face of Islamist extremism.

"I'm not looking to hang three 17-year-olds who were misguided by someone," Zardari said in a September 2008 interview with me for the Washington Post. "We are fighting for a cause that is larger than us."